AbstractID: 7915 Title: A tool for automatic analysis of prostate motion in cine-MRI Image guided radiotherapy of the prostate is hampered by short-term organ movement. We are therefore measuring in detail the frequency distribution of prostate motion in healthy and patient volunteers. The applied MRI sequence alternates between fast collection of 2D sagittal slices and a flash 3D acquisition. In each experiment, over 1000 2D images are collected. The purpose of this paper is to develop a system for automatic analysis of these images. The procedure works as follows: First, a reference image is selected; motion is measured relative to this image. Next, a region of interest is defined in the reference image closely around the prostate and seminal vesicles. Finally, this region is matched automatically (using rigid grey value matching in 2D, for translation and rotation) to each follow-up image. We compared several match criterea and found that minimization of the RMS pixel value differences works most reliable. There are less than 1% match failures for detecting the prostate position. Matching requires a few seconds per image on a standard PC. For efficient review of the analysis, cine-loops are created of the registered followup images. If necessary, failed matches can be corrected manually or can be restarted with different parameters. As end result, the program produces plots of 2D translation and rotation as function of time. The accuracy is better than 1 mm in comparison with manual measurements on point data. We are currently testing the same approach for analysis of the 3D data.